1. Technical Field
The present invention relates to a tailor welded blank which is manufactured by connecting blanks of different materials or thicknesses, a manufacturing method thereof, and a hot stamped part component using the tailor welded blank. More particularly, the present invention relates to a tailor welded blank capable of preventing occurrence of quality problems in a welded zone, a manufacturing method thereof, and a hot stamped component using the tailor welded blank.
2. Description of the Related Art
Respective parts of a vehicle employ various components having different strengths according to functions thereof. For example, a vehicle part for absorbing impact upon collision may employ components having relatively low strength, and a vehicle part required to maintain its shape for securing a survival space for occupants may employ components having relatively high strength.
When a shock-absorbing part of a vehicle has high strength, the shock-absorbing part transfers impact to other parts instead of suitably absorbing the impact upon collision, whereby occupants and other vehicle parts can be exposed to excessive impact.
To fulfill continuous demand for weight and cost reduction in the field of vehicles, a single component is required to have different strengths according to sections thereof.
That is, some sections of a component are required to have relatively high strength for protection of occupants, and other sections thereof are required to have relatively low strength for impact absorption.
One example of such a component includes a B-pillar of a vehicle.
FIG. 1 is an enlarged perspective view of a chassis and a B-pillar of a vehicle.
In a certain car, a B-pillar 1 is disposed between a front door and a rear door and connects a bottom surface of a chassis to a roof.
In the B-pillar 1, an upper portion 1a is required to have a higher tensile strength than a lower portion 1b thereof. The reason for the provision of differences in strength according to sections of the B-pillar provided as a unitary component is because there are two sections in the unitary component, i.e. a structural section (for example, an upper portion required to support a vehicle roof when the vehicle overturns) that needs to maintain its shape upon collision and a shock-absorbing section (for example, a lower portion having a high possibility of lateral collision with other vehicles) that needs to be crushed to absorb shock.
That is, the upper portion 1a of the B-pillar 1 needs high strength because it needs to maintain its shape upon vehicle collision in order to secure a safe space to prevent occupant injury, whereas the lower portion 1b of the B-pillar 1 needs relatively low strength because it needs to be deformed to absorb impact upon vehicle collision. If the lower portion 1b of the B -pillar 1 has high strength as in the upper portion 1a, the lower portion 1b of the B-pillar 1 cannot absorb impact upon lateral collision, whereby impact can be transferred to other structural members.
Although detailed strength can vary according to types or shapes of vehicles, the upper portion 1a of the B-pillar 1 needs a tensile strength of about 1500 MPa, and the lower portion 1b of the B-pillar 1 needs a tensile strength of about 500 to 1,000 MPa.
In the related art, a component is first made of a low strength material and a separate reinforcing material is attached to a section required to have high strength. Further, when a unitary component is required to have different strengths according to sections, a material having high hardenability (or a thick material) and a low strength material having low hardenability (or a thin material) are laser-welded to form a blank, followed by forming a final product through hot stamping.
A blank manufactured by laser-welding components of different materials (or thicknesses) is referred to as a tailor welded blank, which may also be manufactured using a coated steel plate.
When the coated steel plate is laser-welded, a composition material of a coating layer is fused and enters a molten pool of a welded zone, whereby the welded zone has different physical properties than a base material thereof.
For example, when the coating layer is an Al—Si or Zn-based layer, coating components can enter the welded zone upon laser-welding, thereby causing deterioration in physical properties of the welded zone.
In the related art, laser welding is performed after removing a coating layer from a section to be subjected to laser welding, thereby preventing the coating components from intruding into the welded zone. However, this method causes increase in manufacturing costs due to addition of a process of removing the coating layer.
One example of a background technique is disclosed in Korean Patent Publication No. 10-2009-0005004A (published on Jan. 12, 2009), entitled “Method for manufacturing a weld component with very high mechanical characteristics from a coated lamination sheet”.